Display panel module with improved bonding structure and method of forming the same

ABSTRACT

A display panel module includes a substrate, a circuit board, electrode terminals aligned in a first direction over a surface of the substrate, each of the electrode terminals extending in a second direction perpendicular to the first direction, lead terminals aligned in the first direction over a confronting surface of the circuit board to the substrate, at least an anisotropically conductive film sandwiched between the electrode terminals and the lead terminals, and a plurality of first electrically insulating walls on the substrate in at least selected plural ones of gaps between selected ones of the electrode terminals and on opposite side regions of the module, the opposite side regions being distanced in the first direction and separated by a center region. The first electrically insulating walls have a first height that is higher than a first total height of the electrode terminals and the anisotropically conductive film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a display panel module and amethod of forming the same, and more particularly to a display panelmodule having an improved connection structure between a display paneland a circuit board and a method of forming the same.

[0003] 2. Description of the Related Art

[0004] Flat display panels of various types such as liquid crystaldisplay panels, plasma display panels and electroluminescent displaypanels have been well-known to persons skilled in the above-describedfield. Such a display panel comprises an insulating substrate which haselectrode terminals. The display panel forms a display panel module incombination with a flexible printed circuit board for driving thedisplay panel. The display panel and the circuit board are electricallyconnected to each other through the following connection structure.

[0005] The display panel has electrode terminals. The circuit board haslead terminals. The display panel and the circuit board sandwich ananisotropically conductive sheet, so that the electrode terminals andthe lead terminals are spatially separated by the anisotropicallyconductive sheet but electrically connected to each other through thesheet. Japanese Patent No. 2964730 discloses a plasma display panelhaving such a connection structure.

[0006]FIG. 1 is a fragmentary cross sectional elevation view of a plasmadisplay panel module with a conventional connection structure. Theplasma display panel module comprises a plasma display panel and aflexible printed circuit board 5. The plasma display panel has asupporting substrate 1 which has a surface, on which electrode terminals2 and insulating barrier layers 12 are provided, wherein adjacent two ofthe electrode terminals 2 are separated by the insulating barrier layer12. The electrode terminals 2 has a lower height than the insulatingbarrier layer 12. The flexible printed circuit board 5 has a surfacehaving an alignment of lead terminals 6 which are positioned incorrespondence with the electrode terminals 2.

[0007] The plasma display panel and the circuit board 5 sandwich ananisotropically conductive film 4 which has conductive particles 15, sothat the electrode terminals 2 and the corresponding lead terminals 6are spatially separated by the anisotropically conductive film 4 butelectrically connected to each other through the conductive particles 15in the anisotropically conductive film 4. Since adjacent two of theconductive particles 15 are separated, the anisotropically conductivefilm 4 is conductive in a film thickness direction but insulative in anin-plane direction. For this reason, adjacent two of the electrodeterminals 2 are electrically isolated and other adjacent two of the leadterminals 6 are also isolated.

[0008] The electrode terminals 2 are made of silver. The insulatingbarrier layers 12 are provided for preventing that the electricalisolation between the adjacent two of the electrode terminals 2 isdeteriorated by silver migration upon a heat treatment which is carriedout for a thermal compression bonding process for bonding the substrate1 and the circuit board 5 through the film 4. Assuming that the aboveinsulating barrier layers 12 are not provided, then the silver migrationmay be caused via a migration path of a binder for the material of thefilm 4, wherein the migration path is present at a gap between theadjacent two of the electrode terminals 2.

[0009] Advanced displays have narrowed alignment-pitches of theelectrode terminals and the lead terminals. Narrowing suchalignment-pitches causes such an inter-electrode migration easily. Theprovision of the above insulating barrier layers 12 is effective tosuppress the migration. The inter-electrode migration causes a shortcircuit between the electrode terminals. Such a migration is graduallycaused during a long term operation of the display. The reason for theshort circuit between the electrode terminals is not only the migrationbut also other factors on the manufacturing processes.

[0010] One of the other reasons is a difference in thermal expansioncoefficient between the substrate 1 and the flexible printed circuitboard 5. As described above, the substrate 1 and the flexible printedcircuit board 5 are bonded through the anisotropically conductive film 4by the thermal compression bonding process. The flexible printed circuitboard 5 is made of an organic material such as polyimide which has athermal extension coefficient of about 26×10⁻⁶/° C. The supportingsubstrate 1 is made of a transparent glass material which has a thermalextension coefficient of about 5×10⁻⁶/° C. Namely, the flexible printedcircuit board 5 has a higher thermal extension coefficient byapproximate five times than the supporting substrate 1.

[0011] Upon receipt of the heat in the thermal compression bondingprocess, the flexible printed circuit board 5 shows a larger expansionthan the supporting substrate 1. FIG. 2 is a fragmentary perspectiveview of the display panel module after the thermal compression bondingprocess, wherein the electrode terminals of the substrate and the leadterminals of the circuit board have become misaligned due to thosedifference in thermal expansion coefficient. Before the thermalcompression bonding process, the electrode terminals of the substrateand the lead terminals of the circuit board are just aligned. Thethermal compression bonding process causes the substrate and the circuitboard to show different thermal expansions, whereby the electrodeterminals of the substrate and the lead terminals of the circuit boardbecome different in pitch, resulting in a misalignment between them. Thedegree of the misalignment is larger at the opposite end portions thanthe center portion. A large relative displacement between the electrodeterminals and the lead terminals causes a short circuit, whereinadjacent two of the electrode terminals are electrically connected toeach other through the lead terminal having both edges in contact withedges of the adjacent two electrode terminals. Narrowing the terminalpitch reduces such a critical relative displacement, which causes theshort circuit. Increasing the number of the terminals increases therelative displacement at the opposite end portions. The advanced displaymodule has the serious problem with the short circuit formation.

[0012] Japanese laid-open patent publication No. 5-249479 discloses thefollowing conventional technique for avoiding such a short circuitformation between the terminals. FIG. 3 is a schematic perspective viewof a flexible printed circuit board with a single slit at a center. Theflexible printed circuit board 5 has a single slit 14 at a centerposition. The flexible printed circuit board 5 also has a surface onwhich plural lead terminals 6 are aligned. The single slit 14 extends inparallel to a longitudinal direction of the lead terminals 6 and inperpendicular to an alignment direction of the lead terminals 6. Theslit 14 reduces a thermal expansion of the circuit board 5 in thealignment direction. The slit 14 makes it necessary to do plural timesalignment processes, thereby dropping the productivity of the displaypanel module. The formation of the slit 14 causes the increase of themanufacturing cost. The slit 14 weakens the mechanical strength of thecircuit board 5, thereby reducing the reliability of the display panelmodule.

[0013] In the above circumstances, it had been required to develop anovel display panel module and method of forming the same free from theabove problem.

SUMMARY OF THE INVENTION

[0014] Accordingly, it is an object of the present invention to providea novel display panel module free from the above problems.

[0015] It is a further object of the present invention to provide anovel bonding structure between a display panel and a circuit board freefrom the above problems.

[0016] It is a still further object of the present invention to providea novel method of forming a display panel module free from the aboveproblems.

[0017] It is yet a further object of the present invention to provide anovel method of bonding a display panel and a circuit board free fromthe above problems.

[0018] A first aspect of the present invention is a display panel modulecomprising: a substrate; a circuit board; electrode terminals aligned ina first direction over a surface of the substrate, each of the electrodeterminals extending in a second direction perpendicular to the firstdirection; lead terminals aligned in the first direction over aconfronting surface of the circuit board to the substrate; at least ananisotropically conductive film sandwiched between the electrodeterminals and the lead terminals; and a plurality of first electricallyinsulating walls provided on the substrate and positioned in at leastselected plural ones of gaps between selected ones of the electrodeterminals, and the selected ones of the electrode terminals beingpositioned on opposite side regions of the module, and the opposite sideregions are distanced in the first direction and separated by a centerregion, wherein the first electrically insulating walls have a firstheight, which is higher than a first total height of the electrodeterminals and the anisotropically conductive film.

[0019] The above and other objects, features and advantages of thepresent invention will be apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Preferred embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings.

[0021]FIG. 1 is a fragmentary cross sectional elevation view of a plasmadisplay panel module with a conventional connection structure.

[0022]FIG. 2 is a fragmentary perspective view of the display panelmodule after the thermal compression bonding process, wherein theelectrode terminals of the substrate and the lead terminals of thecircuit board have become misaligned due to those difference in thermalexpansion coefficient.

[0023]FIG. 3 is a schematic perspective view of a flexible printedcircuit board with a single slit at a center.

[0024]FIG. 4 is a fragmentary cross sectional elevation view of adisplay panel module with an improved bonding structure in a preferredembodiment of the present invention.

[0025]FIG. 5 is a fragmentary perspective view of a supporting substrateto be bonded to a flexible printed circuit board through ananisotropically conductive film in the form of a display panel module ofFIG. 4.

[0026]FIGS. 6A through 6E are fragmentary schematic views illustrativeof a method of forming a display panel module in a preferred embodimentin accordance with the present invention.

[0027]FIG. 7 is a plan view of a photo-mask with a light-shieldingpattern and a light-transmitting pattern.

[0028]FIG. 8 is a fragmentary schematic view of a substrate withalignment of electrode terminals and electrically insulating walls in amodified preferred embodiment in accordance with the present invention.

[0029]FIG. 9 is a fragmentary schematic view of a display panel modulein a modified preferred embodiment in accordance with the presentinvention.

[0030]FIG. 10 is a plan view of a photo-mask for forming electricallyinsulating walls over a substrate of a display panel module of FIG. 8.

DETAILED DESCRIPTION

[0031] A first aspect of the present invention is a display panel modulecomprising: a substrate; a circuit board; electrode terminals aligned ina first direction over a surface of the substrate, each of the electrodeterminals extending in a second direction perpendicular to the firstdirection; lead terminals aligned in the first direction over aconfronting surface of the circuit board to the substrate; at least ananisotropically conductive film sandwiched between the electrodeterminals and the lead terminals; and a plurality of first electricallyinsulating walls on the substrate in at least selected plural ones ofgaps between selected ones of the electrode terminals and on oppositeside regions of the module, where the opposite side regions aredistanced in the first direction and separated by a center region,wherein the first electrically insulating walls have a first height,which is higher than a first total height of the electrode terminals andthe anisotropically conductive film.

[0032] It is preferable that the first height of the first electricallyinsulating walls is lower than a second total height of the electrodeterminals, the lead terminals and the anisotropically conductive film,so that a top surface of the first electrically insulating wall is notin contact with the confronting surface of the circuit board.

[0033] It is also preferable that the first electrically insulatingwalls are provided in all gaps between the electrode terminals on theopposite side regions.

[0034] It is further preferable that the first electrically insulatingwalls are provided in all gaps between all the electrode terminals overentire regions of the module.

[0035] It is also preferable that the anisotropically conductive filmextends entirely in the first direction and selectively in the seconddirection, so that the first electrically insulating walls are distancedfrom the anisotropically conductive film in the second direction, andtop surfaces of the first electrically insulating walls are not incontact with the anisotropically conductive film.

[0036] It is also preferable that the anisotropically conductive filmextends entirely in the first and second directions, and top surfaces ofthe first electrically insulating walls are in contact with theanisotropically conductive film.

[0037] It is also preferable that each of the first electricallyinsulating walls is distanced from confronting side edges of adjacenttwo of the electrode terminals.

[0038] It is also preferable that each of the first electricallyinsulating walls is in contact with confronting side edges of adjacenttwo of the electrode terminals.

[0039] It is also preferable that the first electrically insulatingwalls comprise dry resist films.

[0040] It is also preferable that the first electrically insulatingwalls comprise a solidified-paste insulating material.

[0041] It is also preferable to further comprise a plurality of secondelectrically insulating walls provided on the circuit board andpositioned in selected gaps between the lead terminals, wherein theselected gaps between the lead terminals are different from confrontinggaps to the first electrically insulating walls, and the secondelectrically insulating walls have a second height, which is higher thana third total height of the lead terminals and the anisotropicallyconductive film.

[0042] It is also preferable that the second height of the secondelectrically insulating walls is lower than a second total height of theelectrode terminals, the lead terminals and the anisotropicallyconductive film, so that a top surface of the second electricallyinsulating wall is not in contact with the surface of the substrate.

[0043] It is also preferable that each of the second electricallyinsulating walls is distanced from confronting side edges of adjacenttwo of the lead terminals.

[0044] It is also preferable that each of the second electricallyinsulating walls is in contact with confronting side edges of adjacenttwo of the lead terminals.

[0045] It is also preferable that the second electrically insulatingwalls comprise dry resist films.

[0046] It is also preferable that the second electrically insulatingwalls comprise a solidified-paste insulating material.

[0047] A second aspect of the present invention is a display panelmodule comprising: a substrate; a circuit board; electrode terminalsaligned in a first direction over a surface of the substrate, each ofthe electrode terminals extending in a second direction perpendicular tothe first direction; lead terminals aligned in the first direction overa confronting surface of the circuit board to the substrate; at least ananisotropically conductive film sandwiched between the electrodeterminals and the lead terminals; and a plurality of first electricallyinsulating walls on the circuit board in at least selected plural onesof gaps between selected ones of the lead terminals and on opposite sideregions of the module, where the opposite side regions are distanced inthe first direction and separated by a center region, wherein the firstelectrically insulating walls have a first height, which is higher thana first total height of the lead terminals and the anisotropicallyconductive film.

[0048] It is preferable that the first height of the first electricallyinsulating walls is lower than a second total height of the electrodeterminals, the lead terminals and the anisotropically conductive film,so that a top surface of the first electrically insulating wall is notin contact with the surface of the substrate.

[0049] It is also preferable that the first electrically insulatingwalls are provided in all gaps between the lead terminals on theopposite side regions.

[0050] It is further preferable that the first electrically insulatingwalls are provided in all gaps between all the electrode terminals overentire regions of the module.

[0051] It is also preferable that the anisotropically conductive filmextends entirely in the first direction and selectively in the seconddirection, so that the first electrically insulating walls are distancedfrom the anisotropically conductive film in the second direction, andtop surfaces of the first electrically insulating walls are not incontact with the anisotropically conductive film.

[0052] It is also preferable that the anisotropically conductive filmextends entirely in the first and second directions, and top surfaces ofthe first electrically insulating walls are in contact with theanisotropically conductive film.

[0053] It is also preferable that each of the first electricallyinsulating walls is distanced from confronting side edges of adjacenttwo of the lead terminals.

[0054] It is also preferable that each of the first electricallyinsulating walls is in contact with confronting side edges of adjacenttwo of the lead terminals.

[0055] It is also preferable that the first electrically insulatingwalls comprise dry resist films.

[0056] It is also preferable that the first electrically insulatingwalls comprise a solidified-paste insulating material.

[0057] It is also preferable to further comprise a plurality of secondelectrically insulating walls provided on the substrate and positionedin selected gaps between the electrode terminals, wherein the selectedgaps between the electrode terminals are different from confronting gapsto the first electrically insulating walls, and the second electricallyinsulating walls have a second height, which is higher than a thirdtotal height of the electrode terminals and the anisotropicallyconductive film.

[0058] It is also preferable that the second height of the secondelectrically insulating walls is lower than a second total height of theelectrode terminals, the lead terminals and the anisotropicallyconductive film, so that a top surface of the second electricallyinsulating wall is not in contact with the surface of the circuit board.

[0059] It is also preferable that each of the second electricallyinsulating walls is distanced from confronting side edges of adjacenttwo of the electrode terminals.

[0060] It is also preferable that each of the second electricallyinsulating walls is in contact with confronting side edges of adjacenttwo of the electrode terminals.

[0061] It is also preferable that the second electrically insulatingwalls comprise dry resist films.

[0062] It is also preferable that the second electrically insulatingwalls comprise a solidified-paste insulating material.

[0063] A third aspect of the present invention is a method of forming adisplay panel module, comprising the steps of: forming an alignment ofelectrode terminals in a first direction over a surface of a substrate,each of said electrode terminals extending in a second directionperpendicular to said first direction; forming electrically insulatingwalls in at least selected plural ones of gaps between selected ones ofsaid electrode terminals on opposite side regions of said module, andsaid opposite side regions being distanced in said first direction andseparated by a center region; forming at least an anisotropicallyconductive film over said electrode terminals; and bonding saidelectrode terminals through said anisotropically conductive film to leadterminals which are aligned in said first direction over a confrontingsurface of a circuit board to said substrate, wherein said electricallyinsulating walls have a first height, which is higher than a first totalheight of said electrode terminals and said anisotropically conductivefilm.

[0064] This third aspect of the present invention has the samecharacteristics described above in connection with the first aspect ofthe present invention.

PREFERRED EMBODIMENTS

[0065] A preferred embodiment according to the present invention will bedescribed in detail with reference to the drawings. FIG. 4 is afragmentary cross sectional elevation view of a display panel modulewith an improved bonding structure in a preferred embodiment of thepresent invention. FIG. 5 is a fragmentary perspective view of asupporting substrate to be bonded to a flexible printed circuit boardthrough an anisotropically conductive film in the form of a displaypanel module of FIG. 4.

[0066] A display panel module has a supporting substrate 1 and aflexible printed circuit board 2. The supporting substrate 1 istransparent. The supporting substrate 1 has a thickness of 1.1millimeters. Electrode terminals 2 are provided on a surface of thesupporting substrate 1. The electrode terminals 2 are aligned at aconstant pitch of 0.12 millimeters in a first direction which isparallel to a longitudinal direction of the supporting substrate 1 andthe flexible printed circuit board 2. Each of the electrode terminals 2has a stripe-shape having a longitudinal direction parallel to in asecond direction perpendicular to the first direction. Each of theelectrode terminals 2 has a width of 80 micrometers. 242 of theelectrode terminals 2 are provided. The electrode terminals 2 are madeof a transparent conductive material, for example, indium tin oxide. Theelectrode terminals 2 have a thickness of 100 nanometers.

[0067] Lead terminals 6 are provided on a confronting surface of theflexible printed circuit board 5 to the supporting substrate 1. The leadterminals 6 are aligned in the first direction at the same constantpitch as of the electrode terminals 2, so that the lead terminals 6 arepositioned in correspondence with the electrode terminals 2. Each of thelead terminals 6 has a stripe-shape having a longitudinal directionparallel to in the second direction. Each of the lead terminals 6 hasthe same width as the electrode terminals 2. The same number of the leadterminals 6 as the electrode terminals 6 are provided. The leadterminals 2 have a thickness of 35 micrometers.

[0068] An anisotropically conductive film 4 is provided, which issandwiched between the electrode terminals 2 and the lead terminals 6.The anisotropically conductive film 4 has a stripe-shape and a width of2 millimeters. The anisotropically conductive film 4 has a thickness of20 micrometers. The anisotropically conductive film 4 extends in thefirst direction along a longitudinal center line of the supportingsubstrate 1 and the flexible printed circuit board 5, so that centerregions of all of the electrode terminals 2 and center regions ofcorresponding all of the lead terminals 6 sandwich the anisotropicallyconductive film 4.

[0069] Electrically insulating walls 3 are provided on the supportingsubstrate 1 and positioned in all gaps between the electrode terminals 2aligned over the entire regions of the supporting substrate 1. Asdescribed above, the stripe-shaped anisotropically conductive film 4with the width of 2 millimeters extends along the longitudinal centerline of the supporting substrate 1 or the flexible printed circuit board5. The anisotropically conductive film 4 overlies, on the longitudinalcenter region, the alternate-alignment of the electrode terminals 2 andthe gaps between them. The anisotropically conductive film 4 does notoverly opposite side regions of the longitudinal center region of thesubstrate 1. The electrically insulating walls 3 are provided in thegaps between the electrode terminals 2 but on the opposite side regionsof the longitudinal center region of the substrate 1. In each of thegaps between the electrode terminals 2, a pair of the electricallyinsulating walls 3 are provided at opposite sides of the anisotropicallyconductive film 4. The paired electrically insulating walls 3 aredistanced by 3 millimeters from each other in the second direction, sothat the paired electrically insulating walls 3 are distanced fromopposite side edges of the anisotropically conductive film 4 having thewidth of 2 millimeters.

[0070] Dual alignments of the electrically insulating walls 3 has thesame pitch of the electrode terminals 2 and the lead terminals 6. Eachof the electrically insulating walls 3 has a width of 20 micrometers anda length of 1 millimeters, wherein the width is a size in the firstdirection and the length is a size in the second direction. As describedabove, the pitch of the electrode terminals 2 is 120 micrometers, andthe electrode terminals 2 have a width of 80 micrometers, for whichreason the gap between adjacent two of the electrode terminals 2 has awidth of 40 micrometers in the first direction. In the gap of 40micrometers, each of the electrically insulating walls 3 of the width of20 micrometers is provided, so that opposite side faces of each of theelectrically insulating walls 3 are separated from confronting sidefaces of the adjacent two electrode terminals 2.

[0071] The electrically insulating walls 3 have a thickness or height of25 micrometers. As described above, the thickness of the electrodeterminals 2 is 0.1 micrometer. The thickness of the anisotropicallyconductive film 4 is 2.0 micrometers. The thickness of the leadterminals 6 is 35 micrometers. The top level of the electricallyinsulating walls 3 is higher by 23 micrometers than the top level of theanisotropically conductive film 4. Thus, the top surface of theelectrically insulating walls 3 is distanced by 12 micrometers from thesurface of the flexible printed circuit board 5. The top level of theelectrically insulating walls 3 fixed on the supporting substrate 1 ishigher by 23 micrometers than the bottom level of the lead terminals 6fixed on the flexible printed circuit board 5.

[0072] The above supporting substrate 1 and the flexible printed circuitboard 5 are bonded by a thermal compression bonding process. Thisthermal compression bonding process causes the substrate and the circuitboard to show different thermal expansions. The electrically insulatingwalls 3 fixed on the supporting substrate 1 prevents a large relativedisplacement between the electrode terminals 2 and the lead terminals 6upon receipt of a heat by the thermal compression bonding process. Therelative displacement is strictly limited by the electrically insulatingwalls 3, thereby suppressing any short circuit between the adjacent twoelectrode terminals 2 and between the adjacent two lead terminals 6.

[0073] The electrically insulating walls 3 prevent such a short circuiteven when the terminal pitch is narrowed and the number of the terminalsis increased. The electrically insulating walls 3 make the advanceddisplay module with the shortened pitch and the increased number of theterminals free from such a serious problem for the conventional displaymodule.

[0074] A method of forming the above display panel module willsubsequently be described. FIGS. 6A through 6E are fragmentary schematicviews illustrative of a method of forming a display panel module in apreferred embodiment in accordance with the present invention.

[0075] With reference to FIG. 6A, an indium tin oxide film having athickness of 100 nanometers is deposited by a sputtering method over asurface of the transparent supporting substrate 1 which has a thicknessof 1.1 millimeters. The indium tin oxide film is selectively etched by alithography technique to form 242 of stripe-shaped indium tin oxideelectrode terminals 2 which are aligned at a constant pitch of 120micrometers over the entire region of the substrate 1 in the firstdirection which is in parallel to the longitudinal direction of thesubstrate 1, wherein the electrode terminals 2 have a width of 80micrometers which is a size in the first direction, and gaps between theelectrode terminals 2 is 40 micrometers.

[0076] With reference to FIG. 6B, a negative dry resist film 7 having athickness of 25 micrometers is adhered by a laminator over an entireregion of the substrate 1 with the electrode terminals 2 underconditions of a temperature of 85-115° C., a pressure of 2-4 kg/cm², anda rate of 1-3 meters/minute. A photo-mask 8A is placed over thesubstrate 1 for irradiation of an ultraviolet ray 9 through thephoto-mask 8A onto the negative dry resist film 7, wherein theultraviolet ray 9 has a wavelength in the range of 350-450 nanometers.

[0077]FIG. 7 is a plan view of a photo-mask with a light-shieldingpattern and a light-transmitting pattern. The photo-mask 8A has alight-shielding pattern 11A and a light-transmitting pattern 10A. Thephoto-mask 8A comprises a transparent substrate with opaque patterns asthe light-shielding pattern 11A and gaps between the light-transmittingpattern 10A as the light-transmitting pattern 10A. Thelight-transmitting pattern 10A comprises dual alignments ofstripe-shaped slits aligned in the first direction, wherein thelongitudinal direction of the stripe-shaped slits is in parallel to thesecond direction. The stripe-shaped slits are aligned at a constantpitch of 120 micrometers. The stripe-shaped slits have a width of 20micrometers in the first direction and a length of 1 millimeter in thesecond direction. The dual alignments are distanced by 3 millimeters.When the photo-mask 8A is aligned over the substrate 1, the dualalignments of the stripe-shaped slits of the photo-mask 8A arepositioned over the gaps between the electrode terminals 2. Each pair ofthe stripe-shaped slits of the photo-mask 8A is positioned over each gapbetween the electrode terminals 2.

[0078] The dry resist film 7 is exposed to the ultraviolet ray 9transmitted through the stripe-shaped slits of the photo-mask 8A,whereby exposed parts of the dry resist film 7 become insoluble by across-linking reaction, whilst the remaining parts or the unexposedparts of the dry resist film 7 remains soluble. A development, andsubsequent cleaning and dry processes are carried out to selectivelyremove the soluble unexposed parts of the dry resist film 7, whereby theinsoluble exposed parts of the dry resist film 7 remain as electricallyinsulating walls 3 having the thickness of 25 micrometers. Thedevelopment is carried out using a solution containing Na₂CO₃ at0.8-1.2%. The cleaning process is carried out by a solution containingKOH at 2-4%. The dry process is carried out in a clean oven at 130° C.for 60 minutes.

[0079] With reference to FIG. 6C, dual alignments of the electricallyinsulating walls 3 are formed, which have a distance of 3 millimeters.

[0080] With reference to FIG. 6D, an anisotropically conductive film 4having a thickness of 20 micrometers and a width of 2 millimeters islaminated along a longitudinal center axis of the substrate 1 andentirely in the first direction parallel to the longitudinal centeraxis, so that the anisotropically conductive film 4 overlies theelectrode terminals 2 and these gaps and extends over the longitudinalcenter region between the dual alignments of the electrically insulatingwalls 3. The anisotropically conductive film 4 is fixed by a previousthermal compression using a heat tool under conditions of a temperatureof 80° C., a pressure of 5 kg/cm², and a time duration of 5 seconds.

[0081] With reference to FIG. 6E, a flexible printed circuit board 5with lead terminals 6 is prepared. The lead terminals 6 have a thicknessof 35 micrometers. A separator is peeled from the anisotropicallyconductive film 4. The flexible printed circuit board 5 is placed overthe supporting substrate 1, so that the lead terminals 6 are aligned tothe electrode terminals 2, wherein the anisotropically conductive film 4is sandwiched between the lead terminals 6 and the electrode terminals2. The flexible printed circuit board 5 and the supporting substrate 1are bonded to each other by a thermal compression bonding process usinga heat tool under conditions of a temperature of 170° C., a pressure of30 kg/cm², and a time duration of 20 seconds. The thickness of theanisotropically conductive film 4 is reduced from 20 micrometers into 2micrometers. The lead terminals 6 and the electrode terminals 2 areelectrically connected to each other through the anisotropicallyconductive film 4. The adjacent two electrode terminals 2 areelectrically separated from each other. Also, the adjacent two leadterminals 6 are electrically separated from each other. As a result, thedisplay panel module is formed.

[0082] Immediately after the above thermal compression bonding process,a bonding structure of the display panel module was observed by amicroscope. All corresponding pairs of the lead terminals and theelectrode terminals 2 are aligned without any substantive relativedisplacement due to difference in thermal expansion coefficient betweenthe supporting substrate 1 and the flexible printed circuit board 5.

[0083] The above effect of provision of the electrically insulatingwalls 3 was confirmed by the above observation by the microscope.Namely, the electrically insulating walls 3 fixed on the supportingsubstrate 1 prevent a large relative displacement between the electrodeterminals 2 and the lead terminals 6 upon receipt of a heat by thethermal compression bonding process. The relative displacement isstrictly limited by the electrically insulating walls 3, therebysuppressing any short circuit between the adjacent two electrodeterminals 2 and between the adjacent two lead terminals 6. Theelectrically insulating walls 3 prevent such a short circuit even whenthe terminal pitch is narrowed and the number of the terminals isincreased. The electrically insulating walls 3 make the advanced displaymodule with the shortened pitch and the increased number of theterminals free from such a serious problem for the conventional displaymodule.

[0084] A contact resistance between each pair of the lead terminals 6and the electrode terminals 2 was measured. The measured contactresistance was within a designed acceptable range. This means that theelectrically insulating walls 3 provide no influence to the electricalconnections between the lead terminals 6 and the electrode terminalsthrough the anisotropically conductive film 4. As described above, thethickness of the electrically insulating walls 3 is 25 micrometers whichis lower than a total thickness of the 0.1 micrometer thickness of theelectrode terminals 2, the 2.0 micrometers thickness of theanisotropically conductive film 4, and the 35 micrometer thickness ofthe lead terminals 6. The electrically insulating walls 3 provide noinfluence to the depression of the anisotropically conductive film 4 inthe thermal compression bonding process.

[0085] The anisotropically conductive film 4 has a binder. In thethermal compression bonding process, the binder is melt out from thefilm 4 when the anisotropically conductive film 4 is depressed betweenthe lead terminals 6 and the electrode terminals 2, wherein the gapsunder the anisotropically conductive film 4 serve as escape zones forthe melt binder.

[0086] In accordance with the above descriptions, the electricallyinsulating walls 3 are provided in all gaps between the electrodeterminals 2 which are aligned over the entire regions of the substrate1. It is possible as a modification that the electrically insulatingwalls 3 are selectively provided on opposite side regions of thesubstrate 1, so that the electrically insulating walls 3 are positionedin selected gaps between the selected electrode terminals 2 on theopposite side regions of the substrate 1.

[0087]FIG. 8 is a fragmentary schematic view of a substrate withalignment of electrode terminals and electrically insulating walls in amodified preferred embodiment in accordance with the present invention.FIG. 9 is a fragmentary schematic view of a display panel module in amodified preferred embodiment in accordance with the present invention.

[0088] The electrically insulating walls 3 are positioned in selectedgaps between the selected electrode terminals 2 on the opposite sideregions of the substrate 1. The opposite side regions of the displaypanel module show larger relative displacements than the center regionwhen the thermal compression bonding process is carried out. This meansthat the relative displacement between the electrode terminals 2 and thelead terminals 6 on the side regions of the module is large and it isimportant to suppress the relative displacement on the side regions ofthe module. In this viewpoint, the electrically insulating walls 3 areselectively positioned on the side regions of the module for preventingthe large relative displacement between the electrode terminals 2 andthe lead terminals 6 on the side regions of the module when the thermalcompression bonding process is carried out.

[0089]FIG. 10 is a plan view of a photo-mask for forming electricallyinsulating walls over a substrate of a display panel module of FIG. 8.The photo-mask 8B has a light-shielding pattern 11A and alight-transmitting pattern 10A. The photo-mask 8A comprises atransparent substrate with opaque patterns as the light-shieldingpattern 11B and gaps between the light-transmitting pattern 10B as thelight-transmitting pattern 10B. The light-transmitting pattern 10Bcomprises dual alignments of stripe-shaped slits aligned in the firstdirection, wherein the longitudinal direction of the stripe-shaped slitsis in parallel to the second direction. The stripe-shaped slits arealigned at a constant pitch of 120 micrometers but only on the oppositeside regions. The stripe-shaped slits have a width of 20 micrometers inthe first direction and a length of 1 millimeter in the seconddirection. Two pairs of the dual alignments of the stripe-shaped slitsare formed on opposite side regions. Each paired dual alignments aredistanced by 3 millimeters. When the photo-mask 8B is aligned over thesubstrate 1, the dual alignments of the stripe-shaped slits of thephoto-mask 8B are positioned over the gaps between the electrodeterminals 2 on the opposite side regions. Each pair of the stripe-shapedslits of the photo-mask 8B is positioned over each gap between theelectrode terminals 2.

[0090] In accordance with the above descriptions, opposite side faces ofeach of the electrically insulating walls 3 are distanced from theconfronting side faces of the adjacent two electrode terminals 2. It ispossible as a modification that the width of the electrically insulatingwalls 3 is the same as the gap between the adjacent two electrodeterminals 2 and between the adjacent two lead terminals 6, so that theopposite side faces of each of the electrically insulating walls 3 arein contact with the confronting side faces of the adjacent two electrodeterminals 2, and also confronting side faces of the adjacent two leadterminals 6. The electrically insulating walls 3 fixed on the supportingsubstrate 1 prevents any relative displacement between the electrodeterminals 2 and the lead terminals 6 upon receipt of a heat by thethermal compression bonding process. No relative displacement is allowedby the electrically insulating walls 3, thereby suppressing any shortcircuit between the adjacent two electrode terminals 2 and between theadjacent two lead terminals 6. The electrically insulating walls 3prevent such a short circuit even when the terminal pitch is narrowedand the number of the terminals is increased. The electricallyinsulating walls 3 make the advanced display module with the shortenedpitch and the increased number of the terminals free from such a seriousproblem for the conventional display module.

[0091] In accordance with the above descriptions, the above electricallyinsulating walls 3 comprise the dry resist films. It is possible as amodification that the above electrically insulating walls 3 comprise asolidified-paste insulating material such as a glass paste. Thesolidified-paste insulating material may be applied by a screen printingmethod in the gaps between the electrode terminals 2 for subsequentsolidifying process.

[0092] In accordance with the above descriptions, the electricallyinsulating walls 3 are distanced from the anisotropically conductivefilm 4 in the second direction, and top surfaces of the firstelectrically insulating walls are not in contact with theanisotropically conductive film 4. It is possible as a modification thatthe anisotropically conductive film 4 extends entirely in the first andsecond directions, so that the anisotropically conductive film 4overlies the entire regions of the substrate 1 or the module, and topsurfaces of the electrically insulating walls 3 are in contact with theanisotropically conductive film 4. As described above, the top level ofthe electrically insulating walls 3 is higher than the bottom level ofthe lead terminals 6. The anisotropically conductive film 4 has such ahigh flexibility as having a varying level between over the electrodeterminals 2 and over the electrically insulating walls 3.

[0093] In accordance with the above descriptions, the electricallyinsulating walls 3 are provided fixedly on the supporting substrate 1.It is possible as a modification that electrically insulating walls 3are provided on the flexible printed circuit board 5 and positioned inall gaps between the lead terminals 6 aligned over the entire regions ofthe flexible printed circuit board 5. The stripe-shaped anisotropicallyconductive film 4 with the width of 2 millimeters extends along thelongitudinal center line of the flexible printed circuit board 5. Theanisotropically conductive film 4 overlies, on the longitudinal centerregion, the alternate-alignment of the lead terminals 6 and the gapsbetween them. The anisotropically conductive film 4 does not overlyopposite side regions of the longitudinal center region of the flexibleprinted circuit board 5. The electrically insulating walls 3 areprovided in the gaps between the flexible printed circuit board 5 but onthe opposite side regions of the longitudinal center region of theflexible printed circuit board 5. In each of the gaps between the leadterminals 6, a pair of the electrically insulating walls 3 are providedat opposite sides of the anisotropically conductive film 4. The pairedelectrically insulating walls 3 are distanced by 3 millimeters from eachother in the second direction, so that the paired electricallyinsulating walls 3 are distanced from opposite side edges of theanisotropically conductive film 4 having the width of 2 millimeters.

[0094] Dual alignments of the electrically insulating walls 3 has thesame pitch of the lead terminals 6 and the electrode terminals 2. Eachof the electrically insulating walls 3 has the width of 20 micrometersand the length of 1 millimeters. As described above, the pitch of thelead terminals 6 is 120 micrometers, and the lead terminals 6 have awidth of 80 micrometers, for which reason the gap between adjacent twoof the lead terminals 6 has a width of 40 micrometers in the firstdirection. In the gap of 40 micrometers, each of the electricallyinsulating walls 3 of the width of 20 micrometers is provided, so thatopposite side faces of each of the electrically insulating walls 3 areseparated from confronting side faces of the adjacent two lead terminals6.

[0095] The electrically insulating walls 3 have a thickness or heightwhich is higher than the total thickness of the lead terminals 6 and theanisotropically conductive film 4, so that the bottom level of theelectrically insulating walls 3 is lower than the top level of theelectrode terminals 2.

[0096] The above supporting substrate 1 and the flexible printed circuitboard 5 are bonded by a thermal compression bonding process. Thisthermal compression bonding process causes the substrate and the circuitboard to show different thermal expansions. The electrically insulatingwalls 3 fixed on the flexible printed circuit board 5 prevents a largerelative displacement between the lead terminals 6 and the electrodeterminals 2 upon receipt of a heat by the thermal compression bondingprocess. The relative displacement is strictly limited by theelectrically insulating walls 3, thereby suppressing any short circuitbetween the adjacent two lead terminals 6 and between the adjacent twoelectrode terminals 2.

[0097] The electrically insulating walls 3 prevent such a short circuiteven when the terminal pitch is narrowed and the number of the terminalsis increased. The electrically insulating walls 3 make the advanceddisplay module with the shortened pitch and the increased number of theterminals free from such a serious problem for the conventional displaymodule.

[0098] In accordance with the above modification, opposite side faces ofeach of the electrically insulating walls 3 are distanced from theconfronting side faces of the adjacent two lead terminals 6. It ispossible as a further modification that the width of the electricallyinsulating walls 3 is the same as the gap between the adjacent two leadterminals 6 and between the adjacent two electrode terminals 2, so thatthe opposite side faces of each of the electrically insulating walls 3are in contact with the confronting side faces of the adjacent two leadterminals 6, and also the confronting side faces of the adjacent twoelectrode terminals 2. The electrically insulating walls 3 fixed on theflexible printed circuit board 5 prevent any relative displacementbetween the lead terminals 6 and the electrode terminals 2 upon receiptof a heat by the thermal compression bonding process. No relativedisplacement is allowed by the electrically insulating walls 3, therebysuppressing any short circuit between the adjacent two lead terminals 6and between the adjacent two electrode terminals 2. The electricallyinsulating walls 3 prevent such a short circuit even when the terminalpitch is narrowed and the number of the terminals is increased. Theelectrically insulating walls 3 make the advanced display module withthe shortened pitch and the increased number of the terminals free fromsuch a serious problem for the conventional display module.

[0099] In accordance with the above modification, the electricallyinsulating walls 3 are distanced from the anisotropically conductivefilm 4 in the second direction, and top surfaces of the firstelectrically insulating walls are not in contact with theanisotropically conductive film 4. It is possible as a modification thatthe anisotropically conductive film 4 extends entirely in the first andsecond directions, so that the anisotropically conductive film 4underlies the entire regions of the flexible printed circuit board 5,and bottom surfaces of the electrically insulating walls 3 are incontact with the anisotropically conductive film 4. As described above,the bottom level of the electrically insulating walls 3 is lower thanthe top level of the electrode terminals 2. The anisotropicallyconductive film 4 has such a high flexibility as having a varying levelbetween under the lead terminals 6 and under the electrically insulatingwalls 3.

[0100] Needless to say, the above description present invention may beapplied to any type display panel modules, for example, not only liquidcrystal display panel module but also plasma display panel module andelectroluminescent display panel module.

[0101] Although the invention has been described above in connectionwith several preferred embodiments therefor, it will be appreciated thatthose embodiments have been provided solely for illustrating theinvention, and not in a limiting sense. Numerous modifications andsubstitutions of equivalent materials and techniques will be readilyapparent to those skilled in the art after reading the presentapplication, and all such modifications and substitutions are expresslyunderstood to fall within the true scope and spirit of the appendedclaims.

What is claimed is:
 1. A method of forming a display panel module, comprising the steps of: forming an alignment of electrode terminals in a first direction over a surface of a substrate, each of said electrode terminals extending in a second direction perpendicular to said first direction; forming electrically insulating walls in at least selected plural ones of gaps between selected ones of said electrode terminals, and said selected ones of said electrode terminals being positioned on opposite side regions of said module, and said opposite side regions being distanced in said first direction and separated by a center region; forming at least an anisotropically conductive film over said electrode terminals; and bonding said electrode terminals through said anisotropically conductive film to lead terminals which are aligned in said first direction over a confronting surface of a circuit board to said substrate, wherein said electrically insulating walls have a first height, which is higher than a first total height of said electrode terminals and said anisotropically conductive film.
 2. The method as claimed in claim 1, wherein said first height of said electrically insulating walls is lower than a second total height of said electrode terminals, said lead terminals and said anisotropically conductive film, so that a top surface of said electrically insulating wall is not in contact with said confronting surface of said circuit board.
 3. The method as claimed in claim 1, wherein said electrically insulating walls are provided in all gaps between said electrode terminals on said opposite side regions.
 4. The method as claimed in claim 1, wherein said electrically insulating walls are provided in all gaps between all said electrode terminals over entire regions of said module. 